Previously we have demonstrated that electroplated copper could be engineered to have microstructures at um and nm scales. This paper shows that not all nanograined copper is created equal. Through systematic investigations, significant insight is obtained into the necessary conditions to create a stable nanograined copper that meets the following criteria: 1. microstructure stable over 9 months at ambient storage conditions, 2. textures of the electrodeposited copper do not depend on substrate types and their textures, 3. grain growth increases to micron scale at temperatures above 150 C. Furthermore, we shall introduce a concept of nanograin threshold in the context of RT microstructure stability.